To manufacture integrated circuits involves the formation of metal interconnections isolated between insulator layers. The interconnection provides specific conducting paths for electrical signals moving between semiconductor devices. A metal layer or alloy is usually serves as the interconnection. Devices isolated from one another must first be formed in the silicon substrate. Then, they are interconnected via these interconnections to form some desired circuit function.
Aluminum or aluminum alloy thin film is widely used as the interconnect structure in the manufacture of ICs. In addition, Al is generally used as the top level in a multilevel-metal structure because wire-bonding technology to Al thin films is a well known and characterized process. Further, the addition of alloy materials to Al is used to alleviate well known problems, such as electromigration and spiking. The films of Al for VLSI interconnections are commonly deposited by DC magnetron sputtering. Other materials used for interconnection include tungsten and titanium.
Typically, a dielectric layer must be deposited on the metal layer to electrically isolate one level of conductor from another layer in a multiple layer interconnect structure. The dielectric layer that is formed on the top of the multi-interconnection is called the passivation layer. The purpose of the passivation layer is not only for electric isolation, but also for protecting the interconnect. For example, the passivation layer prevents moisture from penetrating into the device. However, pin holes are often times formed during conventional formation of passivation layers.